The present invention relates generally to oil filter systems, and in particular to remotely mounted oil filter systems.
Oil is the life blood of an internal combustion engine. We ask it to perform a number of tasks, from reducing component wear to maintaining internal cleanliness. While performing their duties, engine oils are exposed to a number of contaminants including abrasive dirt and dust, component wear particles, and carbonaceous material, to name a few. If allowed to freely circulate throughout the engine, these contaminants can accelerate wear and dramatically reduce the engine's life expectancy.
The most common method of controlling such contamination is through the use of a full flow filtration system. In such a system, oil being driven by a pump must pass through a filter before it is directed to the engine components. This ensures that all the oil being supplied to components has been subjected to at least minimal filtration. However, with full flow filtration, a compromising situation exists between the oil's ability to flow through the filter media and the filter's ability to remove particles.
In a full flow filtration system, particulate contaminants are removed from the oil via surface screening. The arrangement of fibers in the filter media results in openings or passages in which the oil may flow. Particles larger than the openings will be retained at the point of entrance to the media. Particles smaller than the openings will be allowed to pass through. Presently available full flow oil filters generally exhibit a 90-95% removal efficiency of particles 40 microns and larger. Although this type of efficiency dramatically reduces the chance of rapid catastrophic damage to the engine caused by the circulation of large particles, it offers minimal protection against wear. Studies have indicated that the majority of engine component wear today is caused by the circulation of particles in the 5-20 micron range. This size particle is much smaller than any conventional full flow filter can remove with any significant efficiency. By a closer arrangement of the media fibers in the filters, an increase in small particle removal efficiency can be obtained. Here, however, is where the compromise comes into play.
As the fiber orientation is made more dense, oil has a more difficult time flowing through it. As the resistance to flow increases, there is a decrease both in flow volume and oil pressure downstream of the filter. To compensate for these reductions, one could increase the surface area of the now more dense filter. In order to obtain a delta pressure (pressure drop across the media) similar to that of a conventional full flow filter and good filtration efficiency of particles of 5-20 microns, the surface area would have to be increased many times. Generally speaking, this would not be practical from the standpoint of size and cost.
Making the situation even more difficult are four trends within the automotive industry. The first trend is a down-sizing of original equipment and replacement filters. This downsizing is due to limited space in the engine compartment and reduced costs associated with smaller filters. Secondly, oil flow rates in automobiles are increasing. In the past, flow rates of 5-6 gallons per minute (G.P.M.) were typical; today 7-8 G.P.M. rates are not uncommon. Thirdly, engine oils are being exposed to a more severe environment. Elevated operating temperatures and emissions recycling have accelerated internal oil contamination. Finally, many of today's full flow filters are located in areas that are difficult to reach for servicing. As with any servicing operation, the possibility of proper and timely servicing decreases as the difficulty of servicing increases.
One method for improving oil filtration is to add a secondary or by-pass filtration system. By-pass filtration is used in conjunction with the existing full flow system and differs in several respects. First, only a small amount of the output of the oil pump is directed to the by-pass filter. The volume is usually between 5-10% of that being supplied to the engine components. Once the oil has passed through the by-pass filter it is returned to the engine. Because the by-pass filter does not handle high flow rates, media density can be much greater. Not only does this allow for improved small particle removal efficiency, but it often allows for removal of other contaminants not generally removed by conventional full flow filtration, for example, water.
Water generally enters the lubrication system as condensation and/or as a by-product of the combustion process. The effects of water on the oil and ultimately the engine can be devastating. Water promotes corrosion and accelerates the formation of additional acidic corrosive compounds. Its presence adversely affects a lubricant's viscosity. Additives within a lubricant can be hydrolyzed along with the formation of emulsions, thereby reducing the lubricant's effectiveness. The greatest concern is when water, held in a lubricant, is allowed to enter between two heavily loaded engine components. Compression of the water due to the loading will generate high heat. In some cases this heat is sufficient to vaporize the water so intensely that component distress occurs. Generally, the material used in the construction of a by-pass filter media and its design allow for much greater removal of water than that afforded by a conventional full flow filtration system alone.
The by-pass filtration systems on the market today do address some of the problems previously mentioned. Improved small particle efficiency and water removal are common benefits. Increased filtration capacity is accomplished by a now greater surface area to trap contaminants. Because hoses are used to bring oil from the engine to the filter and back, an increase in lubricant system volume occurs. Also, the additional external surface of the hoses and filter result in improved heat dispersion and, in turn, reduced oil temperature.
Unfortunately, present by-pass filtration systems do not address all the problems of full flow filtration and have difficulties of their own. For example, the size of the full flow filter and the difficulty in its servicing remain problems. In fact, many by-pass filtration systems use a filter housing to which a replacement cartridge is installed. Changing such a replacement cartridge can, in itself, be a time-consuming and messy task. Merely getting oil to the by-pass filter and back can be a major installation problem.
In most prior art systems, a pressurized oil passage is tapped to bring oil to the by-pass filter. Placing a tee fitting at the oil pressure sending unit is a common practice. Due to a variety of thread sizes on oil pressure sending units, a number of tee fittings and/or adapters are required to allow a system to be universally installed. Also, with more fittings and connections, a greater propensity for leakage exists. In some cases a sandwich adapter is placed between the full flow filter and the engine block. Oil is then diverted to the by-pass filter as it travels toward the full flow filter. As with the oil pressure sending unit, a variety of thread sizes are needed. More importantly, the adapter increases the space needed for the full flow filter. In many cases, this is not acceptable due to limited space near the engine block.
In returning the oil to the engine, there are two common practices. The first is returning it to a nonpressurized area such as a valve cover or oil pan. Generally, this requires punching a hole that will accept a self-tapping fitting. In some cases drilling is required. Either punching or drilling may pose difficulties when attempted in the engine compartment. In some cases oil is returned via a sandwich adapter similar to that previously described.
In order for the sandwich adapter to function as a return oil passage, oil flow to the full flow filter must be restricted. This creates a pressure differential allowing oil to be directed to the by-pass filter from the higher pressure area and returned to the lower pressure area.
Commonly, the restriction which generates the pressure differential is a fixed port that feeds the inlet side of the full flow filter. In order to create a sufficient pressure differential, the port must be relatively small. Because of its size and its fixed construction, the port makes it difficult to maintain sufficient flow and down line pressure should the by-pass filter circuit become inoperable or subjected to high flow rates. The fixed port type of oil return also must deal with the same thread and size problems as mentioned for the sandwich adapter.